Urban angina, urban arrhythmias: carbon monoxide and the heart
A recent study demonstrated that exposure to carbon monoxide gas increases the occurrence of abnormal heart rhythms in patients with coronary artery disease. Previous studies showed that high levels of carbon monoxide exposure can cause myocardial ischemia, or insufficient blood supply to the heart, and impair heart function. New evidence indicates that even low level exposure to carbon monoxide results in increased levels of carboxyhemoglobin, a product of the interaction of carbon monoxide and hemoglobin, the oxygen-carrying pigment of the blood. Similar elevated levels of carboxyhemoglobin are detected in persons who reside in cities or work in high-risk occupations, such as tunnel workers. Adverse effects of carbon monoxide include: decreased oxygen-carrying capacity of the blood; impaired tissue delivery of oxygen and various oxygen-dependent cell processes; enhanced accumulation of blood clotting cells called platelets; increased frequency of abnormal heart rhythms and atherogenesis, the fatty generation and thickening of blood vessels. Because carbon monoxide can worsen myocardial ischemia in patients with coronary artery disease, the level of exposure to carbon monoxide should be considered in the management of such patients. The increased frequency of abnormal heart rhythms and myocardial ischemia, caused by carbon monoxide exposure, may worsen the risk of sudden cardiac death. Studies indicate that individuals who are frequently exposed to high levels of carbon monoxide have higher rates of heart-related deaths than the general population. The interaction between carbon monoxide and other factors that increase the risk of sudden death requires further investigation. In addition, scientific evidence concerning the adverse health effects of common pollutants, such as carbon monoxide, must be considered in the formulation of environmental regulations. (Consumer Summary produced by Reliance Medical Information, Inc.)
Publication Name: Annals of Internal Medicine
Carbon monoxide and cardiovascular disease
Carbon monoxide gas has long been known to be lethal, and death by carbon monoxide poisoning often occurs in fires, industrial accidents, and sometimes as a means of suicide. A study reported in this issue of the Journal which was carried out by a large group of investigators as part of a multicenter project clearly establishes carbon monoxide as a significant factor in the capability of cardiovascular patients to exercise during a treadmill test. The levels of carbon monoxide used in this study were low and are in the range experienced by smokers who smoke one to two packs of cigarettes a day, by passive smokers who remain in an unventilated room, and by workers who are exposed to automobile fumes in an enclosed space (e.g., tunnel workers). The health hazards from this gas are due to its chemical affinity for attachment to hemoglobin (the oxygen-carrying pigment of the blood), which is considerably stronger than the chemical bond between hemoglobin and oxygen. Carboxyhemoglobin is the molecule resulting from the bonding of carbon monoxide to hemoglobin. At concentrations of carbon monoxide as low as 0.01 percent in the air, the resulting concentration of carboxyhemoglobin in the blood is 14 percent. While most of the carbon monoxide in the body is carried by hemoglobin, some 10 to 15 percent is found in non-vascular tissues associated with similar molecules (e.g., myoglobin, an oxygen-carrying pigment found in muscle). The exact pathophysiologic role of the attachment of carbon monoxide to these other compounds is less well understood than its reaction with hemoglobin, and requires continued research.
Publication Name: The New England Journal of Medicine
Short-term effects of carbon monoxide exposure on the exercise performance of subjects with coronary artery disease
Carbon monoxide is a poisonous gas found everywhere, as it is produced by the incomplete combustion of organic or carbon-containing fuels (including gasoline) and cigarette smoke. Carbon monoxide combines with hemoglobin, the blood pigment which is responsible for carrying most of the oxygen in the body. This combination, carboxyhemoglobin, results from a chemical attraction that is stronger than the attraction between hemoglobin and oxygen. This study investigated the effect of carbon monoxide gas on the hearts and exercise performance of 63 men who were known to have coronary heart disease (an arterial condition resulting in decreased blood flow and oxygen to the heart). The gas was presented to individuals at several levels. The lowest level used in the experiment approximated the highest level of carbon monoxide that is permitted by law in the workplace. The highest level of carbon monoxide used in this experiment was that which would produce the level of carboxyhemoglobin that exists in the blood of active smokers. Subjects were examined on four different days when they underwent exercise treadmill testing after being exposed to a mixture of gases containing carbon monoxide (at various levels) or normal room air; the gases were presented in a random order. Significant changes were observed in the patients when assessed by electrocardiograms. The data suggest that low levels of carbon monoxide in the air inhaled by men with coronary artery disease can result in a significant increase in cardiac symptoms and decreased ability to perform exercise.
Publication Name: The New England Journal of Medicine
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